Tiffany is 16 years older than Christopher. For the last four years, Tiffany and Christopher have been going to the same school. Four years ago, Tiffany was 3 times as old as Christopher. How old is Tiffany now?
Explanation: We can use the given information to write down two equations that describe the ages of Tiffany and Christopher. Let Tiffany's current age be $t$ and Christopher's current age be $c$ The information in the first sentence can be expressed in the following equation: $t = c + 16$ Four years ago, Tiffany was $t - 4$ years old, and Christopher was $c - 4$ years old. The information in the second sentence can be expressed in the following equation: $t - 4 = 3(c - 4)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $t$ , it might be easiest to solve our first equation for $c$ and substitute it into our second equation. Solving our first equation for $c$ , we get: $c = t - 16$ . Substituting this into our second equation, we get the equation: $t - 4 = 3($ $(t - 16)$ $ -$ $ 4)$ which combines the information about $t$ from both of our original equations. Simplifying the right side of this equation, we get: $t - 4 = 3t - 60$ Solving for $t$ , we get: $2 t = 56$ $t = 28$.